1. Field of the Invention
The present invention relates to a contents distribution system, in particular, a system for distributing through streaming digital contents data such as music data or moving image data which is reproducible for a predetermined period of time, such that the digital contents data can be reproduced in a terminal in real time.
2. Description of the Related Art
Due to the development of a large-capacity communications network and the advancements in transmission technology in recent years, moving image distribution services are provided for personal computers and mobile telephones. According to the moving image distribution service, data is provided by a streaming method in which the data is received and stored mainly by the reception terminal side while being reproduced in real time, and a data transmission protocol therefor adopts a real-time transport protocol (RTP) as described in Japanese Patent Laid-open Application Publication No. 304286/2003 (hereinafter, referred to as “related art”) According to the RTP, data is reproduced in a reception terminal without regard to a packet which has been lost during the transmission or a packet which has arrived late. In the case of the moving image reproduction, the data can be reproduced even if part of the data is missing, and therefore, missing packets do not need to be retransmitted, which makes it possible to prevent a traffic burst from occurring. Accordingly, a method according to the RTP is effective in moving image distribution.
According to the moving image distribution method according to the related art, however, a packet which has been lost during the transmission or a packet which has been arrived late is ignored by the reception terminal side as described above, with the result that the image quality is degraded, the reproduction is stopped, or further the image lacks in part thereof, leading to a problem that it is impossible to provide moving image contents of high quality. In particular, according to the related art, the moving image distribution is conducted at the initiative of the server side as described above, that is, the distribution is conducted irrespective of the communications status or the capability of the terminal on the reception side, and therefore the above-mentioned problem becomes increasingly prominent. Specifically, in the case of a fixed terminal, there are various communications methods including optical communications, ADSL, and ISDN, which are different in communications speed, and in the case of a mobile phone, the radio wave condition varies depending on the location thereof, which makes it difficult to realize a stable distribution of moving image.